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V-Notch

Hydraulics · FE Reference Handbook section

Hydraulics
8 formulas
10 exam-style examples
~60 min
All Hydraulics lectures

Core formulas for this FE topic

Definitions, applicability, units, assumptions and worked examples for each relation.

Worked exam-style examples

The four ways this section is written on the real exam — thoughts first, then equations, then substitution.

Example 1
Rectangular weir discharge — solve for discharge — V-Notch

A hydraulics problem uses Rectangular weir discharge. Given weir coefficient (C) = 3.2500; weir length (L) = 9.0000 ft; head over weir (H) = 0.9500 ft, determine the discharge (Q) in cfs.

Given

  • weircoefficient(C)=3.2500weir coefficient (C) = 3.2500
  • weirlength(L)=9.0000ftweir length (L) = 9.0000 ft
  • headoverweir(H)=0.9500fthead over weir (H) = 0.9500 ft

Find

discharge (Q), in cfs

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.

  3. Step 3 — List the givens: weir coefficient (C) = 3.2500, weir length (L) = 9.0000 ft, head over weir (H) = 0.9500 ft.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Q=27.0839 cfsQ = 27.0839\ \text{cfs}
  6. Step 6 — Check: returning Q = 27.0839 cfs to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=27.0839 cfsQ = 27.0839\ \text{cfs}

Why the other options are there

  • 54.1678 — kept a factor of two that cancels in the correct rearrangement.
  • 13.5420 — dropped that same factor in the other direction.
  • 29.7923 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 2
Rectangular weir discharge — solve for weir coefficient — V-Notch (2)

A hydraulics problem uses Rectangular weir discharge. Given weir length (L) = 18.0000 ft; head over weir (H) = 1.4500 ft; discharge (Q) = 197.6 cfs, determine the weir coefficient (C).

Given

  • weirlength(L)=18.0000ftweir length (L) = 18.0000 ft
  • headoverweir(H)=1.4500fthead over weir (H) = 1.4500 ft
  • discharge(Q)=197.6cfsdischarge (Q) = 197.6 cfs

Find

weir coefficient (C)

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except C is given, so isolate C symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that C stands alone on the left-hand side.

  3. Step 3 — List the givens: weir length (L) = 18.0000 ft, head over weir (H) = 1.4500 ft, discharge (Q) = 197.6 cfs.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    C=6.2873C = 6.2873
  6. Step 6 — Check: returning C = 6.2873 to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
C=6.2873C = 6.2873

Why the other options are there

  • 12.5745 — kept a factor of two that cancels in the correct rearrangement.
  • 3.1436 — dropped that same factor in the other direction.
  • 6.9160 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 3
Rectangular weir discharge — solve for weir length — V-Notch (3)

A hydraulics problem uses Rectangular weir discharge. Given weir coefficient (C) = 3.0000; head over weir (H) = 1.9500 ft; discharge (Q) = 418.5 cfs, determine the weir length (L) in ft.

Given

  • weircoefficient(C)=3.0000weir coefficient (C) = 3.0000
  • headoverweir(H)=1.9500fthead over weir (H) = 1.9500 ft
  • discharge(Q)=418.5cfsdischarge (Q) = 418.5 cfs

Find

weir length (L), in ft

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except L is given, so isolate L symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that L stands alone on the left-hand side.

  3. Step 3 — List the givens: weir coefficient (C) = 3.0000, head over weir (H) = 1.9500 ft, discharge (Q) = 418.5 cfs.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    L=51.2298 ftL = 51.2298\ \text{ft}
  6. Step 6 — Check: returning L = 51.2298 ft to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
L=51.2298 ftL = 51.2298\ \text{ft}

Why the other options are there

  • 102.5 — kept a factor of two that cancels in the correct rearrangement.
  • 25.6149 — dropped that same factor in the other direction.
  • 56.3527 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 4
Rectangular weir discharge — solve for discharge (case 2) — V-Notch (4)

A hydraulics problem uses Rectangular weir discharge. Given weir coefficient (C) = 3.4500; weir length (L) = 9.0000 ft; head over weir (H) = 0.8000 ft, determine the discharge (Q) in cfs.

Given

  • weircoefficient(C)=3.4500weir coefficient (C) = 3.4500
  • weirlength(L)=9.0000ftweir length (L) = 9.0000 ft
  • headoverweir(H)=0.8000fthead over weir (H) = 0.8000 ft

Find

discharge (Q), in cfs

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.

  3. Step 3 — List the givens: weir coefficient (C) = 3.4500, weir length (L) = 9.0000 ft, head over weir (H) = 0.8000 ft.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Q=22.2176 cfsQ = 22.2176\ \text{cfs}
  6. Step 6 — Check: returning Q = 22.2176 cfs to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=22.2176 cfsQ = 22.2176\ \text{cfs}

Why the other options are there

  • 44.4351 — kept a factor of two that cancels in the correct rearrangement.
  • 11.1088 — dropped that same factor in the other direction.
  • 24.4393 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 5
Rectangular weir discharge — solve for weir coefficient (case 2) — V-Notch (5)

A hydraulics problem uses Rectangular weir discharge. Given weir length (L) = 10.0000 ft; head over weir (H) = 2.0000 ft; discharge (Q) = 391.4 cfs, determine the weir coefficient (C).

Given

  • weirlength(L)=10.0000ftweir length (L) = 10.0000 ft
  • headoverweir(H)=2.0000fthead over weir (H) = 2.0000 ft
  • discharge(Q)=391.4cfsdischarge (Q) = 391.4 cfs

Find

weir coefficient (C)

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except C is given, so isolate C symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that C stands alone on the left-hand side.

  3. Step 3 — List the givens: weir length (L) = 10.0000 ft, head over weir (H) = 2.0000 ft, discharge (Q) = 391.4 cfs.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    C=13.8381C = 13.8381
  6. Step 6 — Check: returning C = 13.8381 to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
C=13.8381C = 13.8381

Why the other options are there

  • 27.6762 — kept a factor of two that cancels in the correct rearrangement.
  • 6.9190 — dropped that same factor in the other direction.
  • 15.2219 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 6
Rectangular weir discharge — solve for weir length (case 2) — V-Notch (6)

A hydraulics problem uses Rectangular weir discharge. Given weir coefficient (C) = 3.1000; head over weir (H) = 2.6000 ft; discharge (Q) = 144.2 cfs, determine the weir length (L) in ft.

Given

  • weircoefficient(C)=3.1000weir coefficient (C) = 3.1000
  • headoverweir(H)=2.6000fthead over weir (H) = 2.6000 ft
  • discharge(Q)=144.2cfsdischarge (Q) = 144.2 cfs

Find

weir length (L), in ft

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except L is given, so isolate L symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that L stands alone on the left-hand side.

  3. Step 3 — List the givens: weir coefficient (C) = 3.1000, head over weir (H) = 2.6000 ft, discharge (Q) = 144.2 cfs.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    L=11.0954 ftL = 11.0954\ \text{ft}
  6. Step 6 — Check: returning L = 11.0954 ft to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
L=11.0954 ftL = 11.0954\ \text{ft}

Why the other options are there

  • 22.1908 — kept a factor of two that cancels in the correct rearrangement.
  • 5.5477 — dropped that same factor in the other direction.
  • 12.2050 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 7
Rectangular weir discharge — solve for discharge (case 3) — V-Notch (7)

A hydraulics problem uses Rectangular weir discharge. Given weir coefficient (C) = 3.2500; weir length (L) = 9.5000 ft; head over weir (H) = 0.8000 ft, determine the discharge (Q) in cfs.

Given

  • weircoefficient(C)=3.2500weir coefficient (C) = 3.2500
  • weirlength(L)=9.5000ftweir length (L) = 9.5000 ft
  • headoverweir(H)=0.8000fthead over weir (H) = 0.8000 ft

Find

discharge (Q), in cfs

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.

  3. Step 3 — List the givens: weir coefficient (C) = 3.2500, weir length (L) = 9.5000 ft, head over weir (H) = 0.8000 ft.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Q=22.0924 cfsQ = 22.0924\ \text{cfs}
  6. Step 6 — Check: returning Q = 22.0924 cfs to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=22.0924 cfsQ = 22.0924\ \text{cfs}

Why the other options are there

  • 44.1847 — kept a factor of two that cancels in the correct rearrangement.
  • 11.0462 — dropped that same factor in the other direction.
  • 24.3016 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 8
Rectangular weir discharge — solve for weir coefficient (case 3) — V-Notch (8)

A hydraulics problem uses Rectangular weir discharge. Given weir length (L) = 12.5000 ft; head over weir (H) = 2.4000 ft; discharge (Q) = 319.5 cfs, determine the weir coefficient (C).

Given

  • weirlength(L)=12.5000ftweir length (L) = 12.5000 ft
  • headoverweir(H)=2.4000fthead over weir (H) = 2.4000 ft
  • discharge(Q)=319.5cfsdischarge (Q) = 319.5 cfs

Find

weir coefficient (C)

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except C is given, so isolate C symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that C stands alone on the left-hand side.

  3. Step 3 — List the givens: weir length (L) = 12.5000 ft, head over weir (H) = 2.4000 ft, discharge (Q) = 319.5 cfs.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    C=6.8745C = 6.8745
  6. Step 6 — Check: returning C = 6.8745 to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
C=6.8745C = 6.8745

Why the other options are there

  • 13.7491 — kept a factor of two that cancels in the correct rearrangement.
  • 3.4373 — dropped that same factor in the other direction.
  • 7.5620 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 9
Rectangular weir discharge — solve for weir length (case 3) — V-Notch (9)

A hydraulics problem uses Rectangular weir discharge. Given weir coefficient (C) = 3.0000; head over weir (H) = 0.5000 ft; discharge (Q) = 142.0 cfs, determine the weir length (L) in ft.

Given

  • weircoefficient(C)=3.0000weir coefficient (C) = 3.0000
  • headoverweir(H)=0.5000fthead over weir (H) = 0.5000 ft
  • discharge(Q)=142.0cfsdischarge (Q) = 142.0 cfs

Find

weir length (L), in ft

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except L is given, so isolate L symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that L stands alone on the left-hand side.

  3. Step 3 — List the givens: weir coefficient (C) = 3.0000, head over weir (H) = 0.5000 ft, discharge (Q) = 142.0 cfs.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    L=133.9 ftL = 133.9\ \text{ft}
  6. Step 6 — Check: returning L = 133.9 ft to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
L=133.9 ftL = 133.9\ \text{ft}

Why the other options are there

  • 267.8 — kept a factor of two that cancels in the correct rearrangement.
  • 66.9394 — dropped that same factor in the other direction.
  • 147.3 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

Example 10
Rectangular weir discharge — solve for discharge (case 4) — V-Notch (10)

A hydraulics problem uses Rectangular weir discharge. Given weir coefficient (C) = 3.2000; weir length (L) = 4.0000 ft; head over weir (H) = 0.8500 ft, determine the discharge (Q) in cfs.

Given

  • weircoefficient(C)=3.2000weir coefficient (C) = 3.2000
  • weirlength(L)=4.0000ftweir length (L) = 4.0000 ft
  • headoverweir(H)=0.8500fthead over weir (H) = 0.8500 ft

Find

discharge (Q), in cfs

Start with the thinking

  • The governing relation printed in this handbook section is Rectangular weir discharge.
  • Everything except Q is given, so isolate Q symbolically first — never rearrange after the numbers are in.
  • Tabulate each given with its unit and confirm the units are consistent with the relation before substituting.
  • Hydraulics items reward recognising the unknown before touching a calculator.

Step-by-step solution

  1. Step 1 — State the governing relation:

    Q=CLH3/2Q = C L H^{3/2}
  2. Step 2 — Rearrange the relation so that Q stands alone on the left-hand side.

  3. Step 3 — List the givens: weir coefficient (C) = 3.2000, weir length (L) = 4.0000 ft, head over weir (H) = 0.8500 ft.

  4. Step 4 — Substitute the given values into the rearranged relation.

  5. Step 5 — Evaluate:

    Q=10.0309 cfsQ = 10.0309\ \text{cfs}
  6. Step 6 — Check: returning Q = 10.0309 cfs to

    Q=CLH3/2Q = C L H^{3/2}

    reproduces the given quantities, and both sides carry the same units.

Answer:
Q=10.0309 cfsQ = 10.0309\ \text{cfs}

Why the other options are there

  • 20.0617 — kept a factor of two that cancels in the correct rearrangement.
  • 5.0154 — dropped that same factor in the other direction.
  • 11.0340 — rounded an intermediate value before the final step.

Reference: FE Reference Handbook — Hydraulics → V-Notch

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